Electrodeposition of chromium



Patented Mar. 4, 1930 UNITED STATES- PATENT OFFICE CHARLES HENRY PROCTOR, OF ARLINGTON, NEW JERSEY, ASSIGNOR TO THE ROESSLER & HASSLACHER CHEMICAL COMIBANY, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK ELECTRODEPOSITION OF CHROMIUM N0 Drawing.

This invention relates to improvements in the electrodeposition of chromium.

The electrolytic baths commonly usedfor plating articles with chromium contain chromic acid and usually include small amounts of sulphate ions. A great variety of addition agents, such as inorganic salts, have been dissolved with the chromic acid in the prior art baths. However, a limitation of these baths is that they do not throw a deposit into the recesses of irregularly shaped articles which are being chromium plated.

I have now found that the presence of a naturally occurring chrome-iron ore, such as chromite, in electrolytic solutions containing chromic acid shortens the time in which deposits can be plated out. The resulting deposits are also whiter and more evenly distributed over the object to be plated than those which have been obtained by the chromic acid baths previously known. 7

My invention also increases thethrowing power of chromic acid baths, shortens the time in which good deposits will begin to appear, and the internal resistance .of the baths is less than that of the previously known chromic acid baths.

Chrome-iron ores are known to contain in general the following oxides in approximately the proportions given:

Chromic oxide (Gr O -65% Iron oxides .(Fe O 20-35% Magnesium oxide (MgO) 4-16% Aluminumoxide AI O 7-20% Silicon dioxide iO 4- 7% The naturally occurringchrome-iron ore, which I prefer to dissolve in my baths, can be obtained commercially in the form of a fine powder, the empiricalformula of which -shows essentially the following oxides or their equivalents in about the proportions given:

Aluminum oxide (A1 0 7-10% Application filed March 9, 1929. Serial No. 345,888.

One example of my successful chromicacid baths is as follows:

lVater 1 gallon Chromic acid 8-48 02. Chrome-iron ore to 1% oz.

(as described above) H Sulphuric acid (60%) to oz.

Anodes of sheet steel orlead may be used and the bath temperature maintained at 95- 120 F. with current densities of 100-125 amps. per sq. ft.

What I claim is:

1. As a new composition, a chromic acid electroplating solution containing chromeiron ore.

2. As a new composition a chromic acid electroplating solution containing, for each gallon of Water, the following ingredients in about the proportions given:

Ghromic acid (CrO 8 to 48 ozs. Chrome-iron ore (commercial) to 1 ozs. Sulfuric acid to ozs.

the chrome-iron ore having essentially the following analysis;

By weight Chrome oxide (C130 48-50% Iron oxide (Fe O 20-25% Silicon oxide (SiO 4- 7% Magnesium oxide (MgO) 12-14% Aluminum oxide (A1 0 740% Signed at New York city, N. Y., in the county of New York and State of New York this 16th day of February, A. D. 1929.

CHARLES HENRY PROCTOR. 

